Housings of electronic and electrical equipment, such as TV sets, CRT, various computers, facsimiles, and word processors, are generally made of flame-retardant styrene resins, e.g., acrylonitrile-butadiene-styrene terpolymers (ABS resins). These flame-retardant styrene resins generally have a heat distortion temperature between 70.degree. and 90.degree. C. at the highest, as measured under a load of 264 psi according to ASTM D648, and the insufficiency in heat resistance frequently causes troubles in some uses or sizes of the products.
Synthetic resins having a heat distortion temperature of 100.degree. C. or higher include polyphenylene oxide resins (PPO) and polycarbonate resins (PC), but they are poor in molding properties. It has been therefore demanded to develop synthetic resins or resin compositions which are inexpensive and excellent in both heat resistance and flame retardancy.
In order to improve molding properties of PPO and PC, it has been proposed to blend PPO or PC with heat-resistant polymers, e.g., styrene-maleimide copolymers, as disclosed in U.S. Pat. Nos. 4,278,775 and 4,160,792. Although these polymer blends exhibit satisfactory heat resistance and molding properties, there still remains the problem of poor flame retardancy.
It has also been proposed to blend vinyl chloride resins with styrene-maleimide copolymers as disclosed in U.S. Pat. No. 4,458,046. This composition is, though excellent in flame retardancy, poor in heat resistance.
It has further been proposed to add a halogen-containing flame retardant, e.g., decabromodiphenyl ether, to styrene-maleimide copolymers as described in U.S. Pat. No. 4,032,509. The composition is, however, insufficient in flame retardancy and liable to drip with fire, a so-called dripping.
It has furthermore been attempted to copolymerize a monomer, e.g., styrene compounds and maleimide compounds, with a halogen-containing comonomer, such as brominated phenylmaleimide compounds as disclosed in U.S. Pat. Nos. 4,609,711 and 4,661,574, and brominated (meth)acrylate compounds as disclosed in U.S. Pat. No. 4,051,311. However, the copolymers should have a large content of the expensive halogen-containing monomer so as to impart sufficient flame retardancy, which is unacceptable for practical use.
Thus, it has been keenly demanded to develop a synthetic resin or a composition thereof which satisfy all the requirements of flame retardancy, heat resistance, impact resistance, and molding properties.